Northerly turning error compass simulating means for grounded aviation trainers



June 6, 1950 K. A. KAIL 2,510,580

NORTHERLY TURNING ERROR COMPASS SIMULATING MEANS FOR GROUNDED AVIATION TRAINERS Filed Aug. 24, 1946 3 Sheets-Sheet 1 FIG.I

KARL A. KAI L IN VEN TOR. Y %m/X 7m ATTORNEY June 6, 1950 K. A. KAIL 2,510,530

' NORTHERLY TURNING ERROR COMPASS SIMULATING MEANS FOR GROUNDED AVIATION TRAINERS Filed Aug. 24, 1946 3' Sheets-Sheet 2 KARL A. KAIL INVENTOR ATTORN EY June 6, 1950 2,510,580

K. A. KAIL NORTHERLY TURNING ERROR COMPASS SIMULATING MEANS FOR GROUNDED AVIATION TRAINERS Filed Aug. 24, 1946 3 Sheets-Sheet 3 KARL A. KAI L INVENTOR.

lay/4 a ATTORNEY Patented June 6, 1950 ICE A NORTHERLY TURNING ERRoR COMPASS SIMULATING MEANS FoR GROUNDED AVIATION TRAINERS Karl A. Kail, Montrose, Pa., assignor to Link Aviation, Inc., Binghamton, N. Y., a corporation of New York Application August 24, 1946, Serial No. 692,744

This invention relatesto improved means for use in rounded aviation trainers for simulating theiu ctioning of a real magnetic compass. in a plane in actual flight, and more particularly relates to means for simulating what iscommonly referred to as northerly turning errorf ,It'is wellknown to those skilled in the art of ,fiying aircraft thatif a plane, is at anyheading south of east or west, when theplane is turning in either direction the compass indication precedes the actual planes heading. On the other hand, if the heading of the plane is north of east or west, when the plane is turning in either direction the compass indication lags behind the actual .plane s heading. In both cases, the lead or lag, as the case may be, is at a maximum when the plane is heading due north or south, and in both casesas the heading of the plane is due east or westthe compass indication, discounting variation and deviation with which this application is not concerned, is also substantially east and west, respectively. V

For example, in the case of a plane in actual flight north of the equator when the plane is on a west heading and it is turning toward the east through north, the compass deflects in a westerly direction by a certain amount, e. g., 30 degrees, soon after the start of the turn, and as the turn continues toward the east, the compass indication continues to lag actual plane heading until about 30 degrees north of east, at whichtime the compass indication accelerates towards an easterly indication so that the compass indicates an easterly heading at about the same time that the plane reaches the actual east heading. As the actual heading of the plane passes south of east, the compass indication precedes the planes heading by a certain number of degrees soon after the east heading is. passed, and maintains this lead until the actual plane heading is about 30 degrees south of west, at which time the compass indication changes slower than actual heading changes, so that when the plane reaches a west heading the compass also indicates flight toward the west, again discounting variation and deviation.

,-;On the other hand, if the plane. is on a west headingand turns towards east. through south, the compass indicationwillprecede the plane heading soon after the west heading is passed, maintain the lead until about-30 degrees south of east,.at which time the indicated change will beslower than the actual vchan'geso that the compass indication and the actual heading agree when theplane'reaches aneasterly heading, and as the plane turns from easttoward west through north, the compass heading will lag the actual heading in a, corresponding pattern until actual heading and compass indication agree when the plane reaches a westerlyheading;

Claims. (01. 35-102) 2 r The magnitude of the lead or lag (northerly turning error), depends on the rate of turn--the faster the rateof turn the greater will be the magnitude of the northerly turning error. It also depends on the type and sensitivity ofthe compass and'the distance of the plane from the equator.

Also, when the plane is taken out of a turn the compass indication is leading or laggingthe actual plane heading except on an east or west heading, and as a result the compass oscillates indiminishing cycles five or six times until it comes to rest on or about the actual plane heading,. discounting again variation and deviation.

It is a principal object of this invention to provide means for use in a grounded aviation trainer whereby the indications of a simulated magnetic compass indicating instrument in the trainer are properly modified to simulate northerly turning error as well as the compass oscillations which occur when the plane heading is terminated at any heading other than east or west.

In order that the detailed nature of this invention may be clearly understood by those skilled in the art, reference is made to the accompanying drawings wherein the preferred embodiment of my invention is disclosed. In the drawings,

Fig. 1 is a general exterior perspective view of one well known type of grounded aviation trainer and inconjunction with which this invention is especially useful.

Fig. 2 is a general perspective view showing the general arrangement of the principal parts of this invention.

' Fig. 3 is a general exterior view of the main unit Of my invention.

Fig. 4 is a general exterior view of the reversible valve assembly.

Fig. 5 is an exploded perspective view of the detailed construction of the reversible valve.

Fig. 5A is a perspective view of the opposite side of the reversible valve rotor from the side shown in Fig. 5.

Fig. 6 is an exploded perspective view of the detailed construction of the heading valve, and

Fig. 7 is a cross-sectional view through the bellows centering and compass oscillating spring coupling assemblies which-are shown in perspective form in Fig. 3.

Referring now to Fig; 1, it will be seen that the stationary base of. the trainer is designated ll] and-the'fuselage l2. The floor of the fuselage rests upon the top'of the universal joint designated generally by Hi, this joint being in turn supare afiixed to the bottom of pedestal [6 as well as to the octagon .2 0-. The forward pitching bellows 24, the rearward pitching bellows v26, the left I 3 banking bellows 28 and the right banking bellows 33 are all shown in Fig. 1. The turning motor is designated 32, and the arms supporting this motor by 34. The left rudder pedal 3%} is oonnected through link 38 to the left end of the rudder ,bar 40 which is pivoted at 42, and the right rudder pedal 44 is connected through link 45 to the opposite end of rudder bar 40. Link 49in turn con nects the right end of rudder bar 40 with the reversing lever 48, pivoted at B, and link 5| connects the other end of lever 49 with the outerend of the arm 52 which is afiixed to the upper leaf 54 of the rudder valve designated generally by 56. The lower leaf of the rudder valve is designated 531 In r1952 the upper leaf 54 of" the rudder valve v 7 pair of atmosphere ports 60 ernfiiiz of this valve is connected h r sma ic li 54. to a ab Source of 6.6;! e'fix low eaf 58% n is co nected through the pneumatic lines (is and 1G with t e, ur n mo or 3? s. W l knQWn to th sl tiiledin theijart, upon a pressing forward ief itru er'hd l "th in 8 moves to rear; through the action ofreversing lever 49 l 'ni'ove's ahead, rotating the upper leaf '54 of he. rudder valve Ed'clockwise as seen from ab ve. Vacuum and air pressure are selectively d it fi irnsht r emi e nes and. w e: turning motor 32 which motor is energized arm 22.. l te t un ve sal Jo 5 fu ela e lil bl 14F2 2 an 3D to t e l fi "unterclol wise as seen from above. This rota- I I as f the lft rudder pedal 361's pressed ahead of its neutral position, and the rate. of sucli turningf'wili depend upon thernagnitiid'of rorw rq'disp aceni nt of the rudder pedal its neutral position. Upon a return of th i df ne' a :5 vti? 1 he t'a si ion, he rotation or fuselage t2} and-"of the other mentioned" elements casesi. W on the othe andfwhen the rightrndder pedal as; new tha ifi ne t a po i e right end or rudder'valve 4i} moves ahead, causing 1. 4.8. t m re n the ame ilr l fi sea. 3? t more to. the re r ul i g ma m ec swise rotation of the upper leaf 5 1 of theirudde'r va thisinstan re ai a d. atm phere are admitted to the turning, motor 312 through. th l nes 1 and 3 1a reverse m ner, and motor 32 is energized to rotate all of the mentioned partsto the right, or clockwise a S .s een from above. The rotation. cont nues as long as the; right rudder pedal 44; is pressed ahead of its neutral position, and, the rotation is at a rate dependent upon the magnitude of the, displacement of the right rudder pedalfrom itsneutral, position. It. will be noted" that upon a, pressing, forward of the left rudder pedal 36 the right rudder pedal '44 moves to the rear, and vice versa, just as. in

the case of-a real plane;

The conventional control wheel. is designated 1-2, and this wheel is held by the Shaft. 14 which is slidably and rotatably mounted within the pedestal "75 positioned t5 the rear of. the instrument panel l8 upon which are mounted a plurality (if-instruments Also, as is well known to those skilld in th' art,forw'ard movement of the Wheel IZ'r'eSiiIts in 'a'c'ollapsing of the bellows 2.4 and in an ipa'risiohof be11ows'25, and the front end-0f signage I2 is lowered Opposite movement of w en; 12 results in 'anopposite functioning of'the bellows 24' andfifif andtli'e-iiose of-fuselage' I2 is raised. A counterclockwise rotation of wheel [2 ate tlie'main' spindle l'S', octagon "2E, cross results in a .contraction of bellows 30 and in an i 28, and the fuselage l2 banks A plurality f steps 82 are provided in order that access to the cockpit-of fuselage l2 may be easily had, A suitable seat (not shown) is provided within fuselage l2'to the rear of wheel 12, which eat-is. oocupifidty the student in the trainer. The instruments upon the instrument panel correspond to the flight instruments of a plane in actual flight, and theseinstruments are designed to properly respond to all fuselage-movements as well as to movements of the simulated engine controls (not shown) in a mannerto simulate the functioning of theinstrumentsot a real plane in response to corresponding planeand engine control movements.

' For a detailed disclosure of all the previously described elements reference is madeto U. S. Patents 1,825,462'and 2,099;857 issued to Edwin A. Link.

Reference is now made to Fig.' 2 wher'e'the spindle 13 which is rotatablymounted within base it is shown. Four cross members 84* which are affixed to the base-Hi are provided; and-affixed to these cross members by means of bolts 88 is the casting 8}}. Uponthe top ofthis casting; is the ring gear 90 which is affixed-to the casting by means 'ot bolts 92. Aeeord-ingly, the ring gear 93 is stationary at all times; The cross arms 22 Whichare afiiX 'ed-to the octagon 20- are'shown in Fig. 2, and in one of these cross arms is placed a sleeve 93 through which passes the fle gible cable sheathing 94; Upon th-lower-end oijthe flexible cable contained within thesheathing- 94 is affixed the pinion gear 95 which meshes with the ring gear 96. a It will be appreciatedthat-as the fuselage 12- rotates; with respect to the statioioary base and the ring gear 90, the gear -96 travels a'roun d the ring gear 90 and rotates the flexible cable contained within the sheathing- 94. The direction of rotationof the flexible cable will, of course, be dependent upon the d-irection of; rotation of 'f uselage l 2-, andthe angular rotatiori of the flexible cable "Will be dependent upon the angular rotation of uselage t2 Sheathing 94 and the cable therewithin lead-tothe unit-95 shown in box form in Fig. 2-. "L'heeonstruction of this unit is shownin Fig. 3

Referring now to Fig.3, the flexible sheathing Bis shownas is the previously mentioned flexible. cable 98; contained therewith-in cable is rotated in response to rotations of th'e previously mentioned pinion 9e. -Tlie-unit 95in Fig. 3 includes a base [00 upon w hich is: affixed the bracket I-B2-by means-of screws-lllt1 The bracket its rotatably supports the shaft I06 which isconnected to the flexible-cable; 98-throughthe coupling I08 so thattheshaft- HlB is rotated; in. response to rotations ofthefiexiblecablefiS; Upon the right end of. shaft L06 isafiixedt the pinion Iiil'which-is meshed with. the gearellzlzain-torder to drive-the same. GearnIiIQ inturrnismfiixed upon the housinglil 4 of-a Selsyntype transmitter designated. generally. by 1.1 5, which-transmitters are wellknowntothose skilledxinthe. art. Upon .the opposite end'ofhousing. 4441mm gears [4:2

are affixeda pluralityfof mutually;insulatedzslip rings l 6- which are electrically connected-tothe rotor and stator coils within; housing-1.44 in a manner whichis'welhknowm'toethose. skilled in the art. A brush H8 is provided for each of the slip rings H6, and the .outer ends of the brushes are supported by the insulating blocks I which in turn may be suitably supported by bracket I02 mounted upon the base I00. Each of the brushes II8 is connected to an electrical conductorvcontained in the cablel22. The cable a casing I28 which is attached to the instrument panel 18 and a dial I graduated N, E, S, and W. Also, dial I30 may be suitably graduated intermediate the cardinal points, just as in the case of a real aircraft compass. The Selsyn receiver I24 includes a conventional output shaft I32 upon which is affixed the needle I34 so that the needle moves over the dial I30. The instrument is also provided with a reference pointer 35 which may be set by means of knob I31 to the indication to be flown, just as in the case of a similar instrumentin a real plane.

Referring back to Fig. 3, the rotor of the Selsyn transmitter whose housing is designated H4 is designated I38. Means for actuating this rotor will be later fully described.

The Selsyn type transmitter H5 and Selsyn type receiver I24 which are electrically connected by cable I22 are of the type that Whenever the rotor I38 of the transmitter moves through a certain number of degrees, the output rotor I32 of receiver I24 has a simultaneous .angular movement of the same magnitude imparted thereto. The electrical connection maybe made so that upon a rotation of the input rotor I38 of the transmitter. in one direction the output shaft I32 ofthe receiver rotates in a selected direction, while reversal of direction of the rotation of the input shaft results ina reversal of direction of the movement of the output shaft. Inasmuch as the output shaft of the receiver is always positioned relative to its housing in accordance with the instant position of the rotor of the transmitter relative to its housing, it will be appreciated that if the input shaft of the transmitter remains stationary, a rotation of the housing of the transmitter will also produce a described parts of this invention, it will be appreciated that as the fuselage I2 turns with respect to the stationary base I0, the pinion 96 is rotated and turns the flexible cable 98 which in turn rotates shaft I06 carrying pinion H0. The gear H2 is rotated as is the housing II4 of the Selsyn transmitter, and through slip rings II6, brushes H8 and cable I22 the output shaft I32 of the rec iver I24 is rotated, moving the compass indicating needle I34 over the face of the dial I30. Accordingly, as the fuselage I2 rotates clockwise as seen from above through a given number f degrees, corresponding tothe-turning rota-real plane to the right, the housing .II4 rotates counterclockwise as seen from the right in Fig. 3, and

needle I34 will move clockwise over the dial I30.

On the other hand, an opposite rotation of fuselage I2 will result in an opposite rotation of housing H 4 and in. an opposite movement of needle :I34 over the dialjI30. It will be appreciated that theapparatus may be designed so that the needle I34 moves over the dial I30 degree for degree of rotation of the fuselage I2.

Accordingly; as the assumed heading of fuselage I2 changes, the magnetic compass indicator I26 properly indicates the change in assumed heading; V 7

Considering now the means of this invention for simulating northerly turning error, reference is made to Fig. "'2 where it will be seen that the forward end of link I40 is connected tothe arm 52 which is afiixed upon the upper section 54 of the rudder valve 56. Upon the rear nd of this link is a conventional compensating assembly designated generally by I42. In order that the detailed nature of the compensating assembly I42 may be better understood, reference is made to Fig. 4 where it will be seen that this assembly includes an outer sleeve I44 which is connected to theouter end of arm I48 by means of stud I46. Within sleeve I44 is a second sleeve I 50. A washer I52 abuts against .the forward end of each of the sleeves I44 and I50, and the rear end of spring, I54 in turn engages this washer. A second washer I56 engages the forward end of spring I54, and a cotter pin I58 limitsthe'forward movement of washer I56 A corresponding washer I52a, spring securely fasten said end upon the arbor I64 of the rotor I66 of the reversible valve designated generally-by I68, which valve is shown in detail in Fig. 5, to which reference is made.

, It will be seen that the reversible valve I68 includes an integral bracket I10 and stationary housing I14 in which is a circular chamber I16. Bracket I10 may be suitably aifixed to the floor oi,

housing It'd. The first of these connections includes the coupling I which is connected through the pneumatic line I82 to the vacuum source 66; the second includes the coupling I 86 which merely vents chamber I16 to the atmosphere; the third includes th coupling I 83 which is connected through the pneumatic line I90 with the heading valve designated generally by I92 in Fig; 3; and the fourth includes the coupling I9 5 which is connected through the pneumatic line I96 with the heading valve I92.

The rotor I66 of the reversible valve I 68 is of a diameter slightly less than the diameter of chamber I16 so that it will fit therewithin in a substantially airtight manner. A groove I98 completely encircles the rotor I66 near the bottom thereof, and a second groove 200 also completely encircles rotor I66 near the top thereof. A pair of tapered grooves 202 and 20 4 are placed in rotor I66 intermediate the grooves I98 and 200, and each of the grooves 202 and 204 extends around rotor I66 for a distance somewhat less than nects the groove 200 With'the tapered groove 202,

"sane similar channel 2m connects the groove 204 with groove l 9;8.. A

,When the rtor l 66.'1s placed 'within the chamher 116 of h ousing 114,,the. lower groove I98 lies oppositethe interior opening of coupling ISll, and thereiorevacuum is present at alItiInes ingroove N18, channel 21:: and the, tapered groove 204. I At the same time, the groove; 200 isin communication with the port [86 which leadsto th atmosphere, and accordingly I atmospheric pressure is present at all times in groove 200', channel 208 and thetaperedgroove 2 02. l

When the rudder pedals 3B and 44 are in; their neutral positions, the, upper leaf .54,of the, rudder valve -56 will b neutralized, and the turning motor32. will be inoperative. At the same time, the link MB will be neutralized as will the rotor 165 ofthe reversible valve 6'68. In this. position the area Zfldbetweenone pair of. the' adjacent ends of the tapered. grooves 202 and 264 will be opposite the opening into chamber J16 connected to coupling 19.4, and. neither atmosphere nor vacwill be. transmitted.v through the pneumatic un ware the-heading-va'lve [-92 ofFig'. 3'. Under the same conditions, the area 201 of the rotor Hi6 Willi)? opposite the opening into chamber, I116 which connects with coupling 88, and neither vacuurn nor atmosphere will. be transmitted through the pneumatic lin I90 to, the heading valve i 92 Inasmuch as the fuselage I2 is not turning wheneverthe rudder valve andthe. reversible valve we are neutralized, it will be appreciated that the indications, given by the magnetic. compass indicator l 26.,wil lremain constant. However, assuming that the left rudder-pedal 36 is pressed ahead of its neutral position; the rightend of rudder bard?) movesv to the. rear as does. the link ,3,. link .moves' aheadflas does linkJ lfi, and the arm. M3 is rotated counterclockwise as seenv from aboveinFigs z; and i. Referring. to, Fig. 5; it will. be apnreoiatdithat the rotor I66 will be moved in the same, direction, andthe atmosphere groove2l2 will' register with thqcounling {Qi so that atmosphere isadmit'ted through-the pneumatic line Hi5 to thelhea'di'ng valvezlzlli of; Figs. 3 and: 6. Atthe same tirfie, the vacuum; groove 284 will, come. into engagement with the coupling I38 and. vacuum, willlbe admitted along pneumatic line ISO to the. heading valve: L92. a L

.thee;ot-her hand, shouldth right rudder pedal 443- be pressed ahead: o-i-its neutral position, it will be: appreciated that the rotor L6H the reversible-,valve i 68 will be rotated clockwise'as seen= jgrom; 1 above; from its neutral, position, the vacuum groove- 253 willcome, into communication with coupling I94 and vacuum will be admitted to the heading valve l9? through pneumatic line Hill: A-tithe same time the atmosphere groove- 202; wi ll register withthe:; coupling-- [88, and; atmosphere will be transrnittedv alongpneumatic line.- lea tothe heading valve 593..

It will also-be appreciated that. the magnitude off atmosphere and vacuum: admittedto thelines H Referenceris now made to -Figs.- 3 andyd which.

disclose the. general position; and detailedconstruction of: the, rotary heading valve;designated generallyzby I32; It will-be seen; that a;brack et 22H is 'afiixedto the base i lllil by imeanssoi screws 222;and: that:the stationarps'jhousingl- 22;!- oithe,

heading valve 32 is integral with bracket 220."

:rhehonsinggm includes 'ac amber 1226- which fourhollow couplings communicating therewith. The first oithese couplings'i's designated 2,25 and. is connected .to, the previo'usly described pneumatic line 499'; the second coupling is 23!] ,is connected to the previously f described pneumatic line E; the'third istheco'upling Z'EZQWHich connects with the pneumatic line 234 as seeninFig. 3, conr'iects to the coupling 72-36 Whichciohrmnnitzates with the interior of the bellows designated-generally by 2 38'; and the fourth is the 'coup1irig'240 which connects through the pneumatic line 242 withfthe' coupling [224 V ,which' communicates with the-interior or, the bellows designated generally 'by-245; A filter 258 is connected through c'oupling 252 with the coupling Z32; arid; a second filter 255' is connected through coupling 25'? with the coupling me, Both of the filtcrsZBiland- 25.4% ,cqm rcate with the"atmosphere, and 'accordinglv; a slight. atmosphericfvent is always provided for reasons tobe explained. t 4

The rotoroi' the heading valve is designated 25!}, and; its construction is substantially identical with'that ofithe rotorlfiof the reversible v'a-l-ve 25,8, Consequently, rotor-25c includes a; pairof grooves 262 and 264' which-completely'encircle the rotor, 3S' W'611"'&S a pair of'tfaper'ed grooves 2'55 and 268 which liein'termediate the grooves 262 and 25 i.v The ends ofthe tapered grooves "256" and 258" are ofis'etffrom one another at-the two points; diametrically opposite points 2'10 (on-131 one, shown), 11 stas inf the caseof the reversible valve shown in Fig; 5,] 'Afchannel' 212 connects the groove 2E2 with the tapered groove 266, While channel 2'l4"co'nnects groove 26 with the taperedigroove' fiii.

The diameter of. the rot0r 2'6fi is slightly less than thegd'iarneter, of the ,chamber2 2-6 so that it fit tner'ewithi ifin aslibstantiall'y airtight fashion-,1 and the outer end of rotor 26!) carries a flangell't ,which engages the lip of housing 22 2; Also, the ,arlbo'rjill'lt integraliwith rotor 263,1 andia collar Elli! maybe afilxed upon the outer endof' arbor Z18 biyrneans' of. set screw"2 '8 2 inlorder to retain the rotor 251!" in" longitudinal cesium. g

The functioning of the heading valve will be laterdescribedh'ereinin detailv Refer-ringsnow; to Fig. 3,. it twill .b'e seen"that thenbellowsfi'fi includes a'lstati'on'ary memb 2 91] a-fiiked to thebracliet,2925 by means ofscrefws 294, bracket. 2 92Lin. turn b'ein'g-affiiied' to the base Hi0 :by-mean s-oliscrews' 298., Tide" movable portion of bellowsliifw isdesignated;298Qand a suitable airtight fab-1103i! iii-renders bellows ZBB'air'tighft. The bellovqsflii includ'esLa stationary member 302, suppontedl like the member 296;; and themember 298 forms the other'side of bellows: 2'45". Fabric 386 also .rendersbellows 2 36 airtight. block 3M is,. affixed uponmthebase I00,gand this block supports one end:- of the rod 3E5.upon v vhi'chgis pivotal ly-mo nntedthe lowerendsof the U. ,pc'd

m.ember 3il8'which encircles the-uppertlireesides of the" common bellowsiormidg", member 258. The othenendlof rod13il6 isTsupported-bybracket teens bestlsee'niiii, Big; 7'. Afjsldt are" is placed in. member 368;. and-1 the outer. e'n'd'of rod 3:12

passes throughithis slot to engage the, U-shaped member .352} is aflixed to: the commonflbe llowsforming rnemberlsfl by meansof screwsj'l 31- memberAs'b'est seefi'in-Eigif '7, the. U sha'ped nefinn lsnlrwnig; 7; it .will Be s'ejenthatthe 1 ca tin 52 stren t 815a? 2 11 i j fi h spring housing 320 is affi ire'dbv means'ofsetfscrew 322. Spring housing 328 houses the flat torsion spring 324, the inner end of which is affixed to the hub 320a of housing 320 and the outer end of which is anchored upon the pin 328 which passes through disc 326 as shown. A second pin 338 also passes through disc 326 and is positioned to be engaged by the pin 332 which is carried by housing 320, as shown. The casting 292 also houses the spring 334, the outer end of which is anchored upon pin 328 and the inner end of which is aflixed to the hub 292a of housing 292. -Spring 334 is identical in construction with spring 324, but it is wound in the opposite direction. A pin 336 is carried by casting 282 to engage the previously mentioned pm 330, under circumstances to be described.

To the left of the just described spring assembly, which for convenience is designated generally by 3I9 and is hereinafter referred to'as the bellows centering assembly, is a spring coupling assembly designated generally by 338 and which includes a spring housing 348 affixed upon shaft 3l8 by means of set screw 342. 'Housing 343 houses the spring 344, the outer end of which is anchored upon pin 346 which passes through disc 348, and the inner end of which is aflixed to the hub 340a of housing 340; A pin 350 is carried by housing 340 and engages thepin 352, which is also carried by disc 348, under circumstances to be later described. A second shaft 354 is aligned with the shaft 358, and upon this shaft is affixed the spring housing356 by means of set screw 358. This housing contains the spring 360, the outer end of which'is afiixed upon the pin'346 and the inner end of-which is affixed to the hub 356a of housing 356; A pin362 is carried by housing 356 to engage the previously described pin 352 under circumstances to be'later described. The springs 344 and 360 are'identical in construction, but are wound in opposite directions for reasons later made apparent.

' Referring -to Fig; 3, it will be seen that the shaft 354 is rotatably mounted in the bracket 364 which may be suitably 'afiixed to the base I80. Upon the left end of shaft 354 there'is mounted the-spur gear 366 which carries the eccentric pin 368 which engages the yoke 318 which in turn is affixed by means of screw 369 upon'the rotor I38 of the Selsyn transmitter I I5.

Also in Fig. '3, it will be seenthat the bracket 364 carries the shaft 312 upon the outerend of which is affixed thapinion3l4 which is driven by gear 366. I Pinion 314 is integral with the spur gear3l6 which in turn'drives the pinion 318 affixed upon shaft 388' whichisrotatably'carried by bracket364. Upon the outer end of shaft 388 is affixed the flywheel 382 which carries a plurality of air engaging blades 384 which damp the action ofthe flywheel 382. w 1

As also seen in Fig. 3,"afiixed to the stator II4 of the Selsyn type-transmitter I I5 isthe shaft 386 upon the left end of which is integrally mounted the coupling member 388- which v engages the pin 390 carried by the rig'htlend of the rotor 260 of the heading valve.

Considering now-the operation of the spring coupling assemblies shown'i'n Figs. 3 and "7,Iit

will be appreciated that whenever bellows 246 is collapsed and "bellows 238expanded, as will be later explained, in detail, the 'U-shaped member 388 carried by 'thecentral' bellows [member 238 will rotate clockwise as seen from the right in Figs. 3 and ,7, f Sucha movement carries the rod 3I2 in the, same direction and thehousing 328 is similarly rotated. The pin :32- engages m 330 and accordingly disc 326 is rotated with the hous ing 328. The spring 324 within housing 320 is also rotated in the same direction, and inasmuch as spring 324 is anchored to disc 326 and to housing 328, this spring will neither be tensioned or relaxed. However, the spring 334 which has its inner end anchored to the stationary housing 292 and its outer end to the pin 326 will be tightened, and will exert a force upon the disc 326 tending to rotate this disc, the housing 320 .and spring 324 back to their neutral positions. However, as long as bellows 246 remains collapsed and bellows 238 remains expanded, the spring 334 will not have sufiicient strength to return the just described parts to their neutral positions. Inasmuch as housing 328 is pinned upon shaft 3I8 by means of pin 322, the shaft 3l8 will be rotated clockwise as seen from the right, and inasmuch as housing 348 is pinned to shaft 3l8 by pin 342, the spring housing 348 will be rotated in the same direction. Pin 358 engages pin 352 and rotates the disc 343 with housing 348, and, of course, spring 344 rotates in the same direction.v The tension upon spring 344 is not changed. *When the pin 352 is rotated clockwise it comes out of engagement with the pin 362, carried by the spring housing 356, and the tension of spring 368 causes the housing 356to be rotated clockwise, slowly, following the housing MIL-until the housing 356 has been rotated through the same angle as housing 340, at which point pin 362 again engages pin 352 and the rotation of housing 356 is stopped. The rotation of housing 356 slightly relaxes the tension upon spring 360. v

The rotation of housing 356 causes a clock wise rotation of shaft 354, and as best seen in Fig. 3, the gear 366 is rotated in the same direction.

'By means of eccentric 368 and coupling 310, the

rotor I38 of transmitter H5 is rotated clockwise, and the operation of the Selsyn type transmitter results in a movement of needle I34 seen in Fig. 2 over dial I30, to modify the reading of the magnetic compass instrument basically dependent upon the actual fuselage heading. r

When the bellows 246 and 238 in Fig. 3 are later neutralized, it will be appreciated without a detions, and the modified reading of the magnetic compass indicator I26 in Fig. 2 is removed from the instrument so that the instrument indicates in accordance with actual fuselageheading. H

It is believed unnecessary to explain" in detail that when bellows 238 is collapsed and bellows 246 is expanded the bellows centering assembly 3I9 operates to cause a counterclockwise rotation of shaft 3| 8,which rotation is transferred to the shaft 354 by means of the spring coupling assembly 338, so that the rotor I38 of stator H4 is rotated counterclockwise, resulting in a modifled compass indication, but in the oppositedirection from that first explained above. Whenthe bellows 238 and 246 are neutralized, the modified indication of the compass indicator is no longe present.

Still referring to Fig. 3, it will be appreciated that whenever gear 366 is rotated in response to a, change in the position of the central bellows member 283, by means of pinion 314,-"gear 31 8,

trainer is rotated from west to'south north to west, etc., when actual fuselage heading is south of west and east, the compass indication properly leads the actual heading, and when the heading is north of east and west, the indicated compass reading lags the actual heading, The lead and lag gradually build up and diminish; just as in the case of a plane. in actual flight, and the magnitude of the lead and lag depend upon the rate of fuselage rotation, just as in the case of a plane in actual flight.

Considering now theoperation of the apparatus of this invention when the trainer is rotating from west to north to east to south to west, etc, it will be appreciated that the reversal of the reversible valve I68 shown in Fig. 4 as a result of the forward'displacement of the right rudder pedal will reverse the vacuum and atmosphere in pneumatic lines I90 and I96, 1. e., the line I90 will be at atmospheric pressure and the line I96 will be supplied with vacuum. Inasmuch as the rotor 260 of the heading valve is always positioned in exactly the same manner for anygiven actual fuselage heading regardless of the direction of turning of the fuselage, it will be appreciated that the bellows 238 and 246 will be positioned for any given fuselage heading exactly opposite their positions as described in detail immediately above. Accordingly, from west to east-through north bellows 238 will be contractedand bellows 246 will be expanded, displacing the rotor I33- counterclockwise of its neutral position. Inasmuch as during this interval the housing H4 of transmitter H is also being rotated counterclockwise, the relative motion between the housing and rotor is decreased, and the compass indication lags the actual heading. 1 1

From east to west through south the bellows 238 will be expanded and bellows 246 will be contracted, displacing rotor I38 clockwise of its neutral position. The movements of housing I I4 and of rotor I38, being inopposite-directions, arcadditive, and so the indication given vby the mag-. netic compass indicator I26 leads the actual fuselage heading.

All of the above assumes-that the plane isifly ing in the Northern Hemisphere. To simulate Southern Hemisphere conditions it is merely necessary to reverse the pneumatic lines I96 and I96. To simulate different distances from the equator, it is merely necessary to vary the effective length of arm I48 in Fig. 4.

It is believed unnecessary to explain in detail that the above outlined functionings properly occur when a turning of thefuselage I2 in either direction is started from any heading.

It has been previously stated that in thev case of an aircraft in actual flight, when the plane is turning upon a heading where the magnetic compass indication leads or lags the actual plane heading, and the plane is taken out of the turn upon such a heading, the magnetic compass indi cation will oscillate several times in diminishing cycles about the actual heading, "and finally come to rest at the actual heading, disregarding the factors of variation and deviation. i

It is to simulate this phase of magnetic com pass operation that the flywheel 382 and the -associated gears of Fig. 3 are employed. It will be appreciated that if the central bellows member 298 is displaced from its neutralposition,'as is the case when a lead or lag indication is being given, and the rotation of fuselage I2 is termi hated, the neutralization of "the reversible valve I68 of Fig. 4 will result in a neutralization of the to east to.

. v14. bellows 238 and 246. ber 298 will be neutralized, resulting in a return of the shaft 354 and gear 366 to its neutral position, under the influence of the assemblies 3| 9 and 338 which also return to their neutral positions. The gear 366 rotates relatively slowly back to its neutral. position, but at a slightly accelerated rate, and it will be appreciated that the reduction gear train interposed between this gear and the pinion 318 will cause the fiywheel382 to rotate much faster at an increasingly rapid rate. Accordingly, when the gear 366 has beenreturned to its neutral position, the inertia of flywheel 382 will carry this gear beyond its neutral position a substantial distance, but not quite as far as it was originally displaced on the other side. This displacement is made possible because of the provision of the spring coupling assembly 338. Dhe displacement of gear .366 past its center position results in a tightening of the spring 360 or 344 of assembly 338 and in a relaxation of the other spring, depending upon the direction of rotation of the flywheel 382. The tightening of one of the springs will eventually stop. the rotation of flywheel 382, and then the two springs 36!] and 344 being out of balance, the shaft 354 Will be rotated in the opposite direction, againpast its neutral position but not as far as the first oscillation past neutral. of the gear 366and interconnecting gears will pass through two or three complete cycles of diminishing magnitude until the flywheel 382 and shaft 354 come to rest, with the springs of assembly 338 in balance at the center stop.

It will be appreciated that the rotor I38 of Selsyn transmitter H5 follows the oscillations of the shaft 354 and flywheel 382, and consequently, the needle I34 of the magnetic compass indicator I26 will oscillate about, the actual heading. and finally come to rest at an indication corresponding to the actual fuselage heading.

The vanes 384 attached to the flywheel 382 are used to dampen the oscillations of the flywheel.

It will be appreciated therefore that the apparatus of this invention provides improved means for use in grounded aviation trainers forv simulating the operation of a magnetic compass indicator in a plane in actual. flight. With the use of the disclosed apparatus, the student re-;

ceiving instruction in the trainer will learn to take into .accountthenortherly turning errors in a real compass.- i

Inasmuch as the preferred embodiment of this inventionhas been disclosed, it will be appreoiatedby those skilled in the art thatmahy' changes may be made in the construction thereof without departing from the substance of this invention nor from the scope of the following "2 claims:

. I claim:

1. In a grounded aviation trainer of the type comprising a pair of pedals simulating the rudder pedals of a real plane and an instrument simulating the magnetic'compass of a real plane, the

combination of a first means responsive to the successive directions, magnitudes'and temporal durations of displacements of said pedals from their neutralpositions for changing the indication of said instrument, and a second means for The central bellows mem- This oscillation of the flywheel 382 and means inter-connecting said rotary heading valve and saidpe'dals for positioning saidheading-valvel inaccorda nce with the successive directions, magnitudes and temporal durations of displacementsiof said pedals from-their neutral positions, and a connection between said rotary heading valve and 'said'instrument whereby the instant modinf ation of said compassreadin'g is dependent upor'fthe instant positions of said reversible andi'otary heading valves 2. Ina grounded aviation trainer of the type comprising a pair of pedals simulating the rudder pedalsaof 'a real' plane and an instrument s'irnulating'the magnetic" compass of a real plane, th combination "of a 'Selsyn transmitting system including a transmitter and a receiver fermen ing said instrument, a first means responsiye to the successive directions, magnitrides and temporal durations of displacements'of said pedals from their neutral positions'conneted to said transmitter for chang its the nuisance of said instrument, and a seco irdjfneans" for modifyin the indication of said compassesaetrmined'by said first means, said seeon'd meansinemaing a'lreversible valve con- V l dals and directionally controlled n of displacement of said pedals, ingfvalve connected to said remeans interconnecting said rotary ing valve jand fsaid pedals for positioning said heading vane; in accordance withthe successivefdirections, magnitudes and temporal durations of displacements of said pedals from their neutral positions, and a connection between saidrotary. l'i eading valve and said transmitter, whereby the instant modification of said compass readingfis dependent upon the instant p sitions offsaid" reversible and rotary heading valves.

3. 1'n a grounded aviation trainer of the type includin a fuselage rotatably mounted Iupon 'a stationarypbase, 'a pair of pedals in the fuselage simulating the rudder pedals of a real plane for controlling the rotation of the fuselage, and

aniristrumgnt in thej fuselage simulating the magnetic compassof areal plane, the combinationof. a first means operable in response to the rotation of said fuselage relative to v said Sta-- tionary base for changing the indication of said instrument, and a second meansfor modifying thel indication of said. compass as determined by said first meansjsaidsecond means including a reversible valve connected to said pedals and directionally controlled by the direction of displacement of said pedals, arotary heading valve operable inresponse to-the rotation ofsaid fuse}- lage.;rel ative, is saidstationary base, to be positionediin; accordance withthe instant orientation of said fuselage relative to said stationary base, a connection between said reversible valveandisaid heading valve, and a connection. betweensaid heading valve and said; instrument, whereby the instanttdnodification; of said compass reading is dependent upon the instant. positions of .said

reversible and rotary heading valves. I

4'. In a grounded aviation trainer ofthe type including a fuselage rotatably mounted upon a stationary base, a pair of pedals in the fuselage' simulating; the rudder pedals ofa real plane for controlling the rotation of the fuse lage, and an instrument in the fuselage simulating the magnetic compass of real plane, the

combinationiof a. Selsyn transmittin system including a transmitter and a receiver for actuating said instrument, laj flrst means operable in response to the; rotation of, said, fuselage relative to.said stationary; base connected to-said;

transmitter, forchaneiin the indication of said instrument, and ausecond meansfor modifying the indication of said compass as-determined by said first..mea-ns', saidsecond means includ-- ing a reversible valve connected to said pedals and directionally controlled by the-direction of displacement of said pedals, a rotary heading valveoperable in: response to the rotation of said fuselage relative to said stationary base to be positioned in-Vaccordance with the instant orientation of said'fuselage relative'to said stationaly base, a connection between said reversible valve-and said-rotary heading valve, and a connection between saidzrotar'y. heading valve and said transmitter, whereby the instant modification of said compass reading is dependent upon the instant positionsof said reversible and rotary valves.

5. In a gr'ounde'daviation trainer of the type comprising a pair ofpedals simulatin the midderlpedals' of a real plane and an instrument simulating the magnetic compass of a real plane, the combination o'f a.first means responsive to the successive directions, magnitudes and temporal durations of displacements ofsaid pedals from their neutral positions for changing the indication of said instrument,- and a second means for modifying the indication of said compass as determined bysaid-first means, said second means including a. reversible valve connected to said pedals and directionally controlled by the direction of displacement of said pedals, a vacuum source and-an atmospheric vent connected to said reversible valve, a; rotary heading valve, a pair of pneumatic lines connecting said reversible valve a'nd said rotary heading valve, means for positioning said rotary headin valve in accordance with the successive di-- rections, magnitudes and temporal durations of displacements of said pedals from their neutral positions, a pneumatically operable member, a pair of pneumatic lines interconnecting said rotary heading, valve and said pneumatically operable member, and a connectionbetween said pneumatically operable member and said instrument whereby the instant modification of said instrument reading isdependent upon the instant pOSitiOnsofsaid' reversible and rotary heading valves.

6. Ina grounded aviation trainer of the type comprising a pair of pedals simulating the rudder pedals ofareal ,plane andan instrument simulating the; magnetic, compass of .a' real plane, the combination of, a; ,Sels'y'n' transmitting system including .a, transmitt'er and a receiver for actuatingsaidinstrument, a vfirst,,mean s responsive to-thensuccessive directions,.-magnitudes and temporal durations :of displacements of said pedals fromatheirv neutral positions. connected to said transmitter for, changing the indication ofsaid: instrument, and a. second means for modiflting the indication-- of said compass as determined bysaidfirst meansusaid second means including, a reversible'valve connectedto said pedals and directionally controlled by the direction of displacementof said pedals, avacuumsourceand an--atmospheric vent connected to said -reverfsiblevalve-a rotaryheading valve, a pair. of--.pneuma-tic; lines: connecting said reversible; -valveand-- said rotary heading valve, meansfon positioning said-g rotary heading valve in accordance with the successive directions, magnitudes and temporal durations of displacements of said pedals from their neutral positions, a pneumatically operable member, a pair of pneumatic lines interconnecting said rotary heading valve and said pneumatically operable member, and a connection between said pneumatically operable member and said transmitter, whereby the instant modification of said instrument reading is dependent upon the instant positions of said reversible and rotary heading valves.

7. In a grounded aviation trainer of'the type including a fuselage rotatably mounted upon a stationary base, a pair of pedals in the fuselage simulating the rudder pedals of a real plane for controlling the rotation of the fuselage, and an instrument in the fuselage simulating the magnetic compass of a real plane, the combination of a first means operable in response to the rotation of said fuselage relative to said stationary base for changing the indication of said instrument, and a second means for modifying the indication of said compass as determined by said first means, said second means including a reversible valve connected to said pedals and directionally controlled by the direction of displacement of said pedals, a vacuum source and an atmospheric vent connected to said reversible valve, a rotary heading valve, a pair of pneumatic lines connecting said reversible valve and said rotary heading valve, means for positioning said rotary heading valve in accordance with the instant orientation of said fuselage relative to said stationary base, a pneumatically operable member, a pair of pneumatic lines interconnecting said rotary heading valve and said pneumatically operable member, and a connection between said pneumatically operable member and said instrument, whereby the instant modification of said instrument reading is dependent upon the instant positions of said reversible and rotary heading valves.

8. In a grounded aviation trainer of the type including a fuselage rotatably mounted upon a stationary base, a pair of pedals in the fuselage simulating the rudder pedals of a real plane for controlling the rotation of the fuselage, and an instrument in the fuselage simulating the magnetic compass of a real plane, the combination of a Selsyn transmitting system including a trans mitter and a receiver for actuating said instrument, a first means operable in response to the rotation of said fuselage relative to said stationary base connected to said transmitter for changing the indication of said instrument, and a second means for modifying the indication of said compass as determined by said first means, said second means including a reversible valve connected to said pedals and directionally controlled by the direction of displacement of said pedals, a vacuum source and an atomspheric vent connected to said reversible valve, a rotary heading valve, a pair of pneumatic lines connecting said reversible valve and said rotary heading valve, means for positioning said rotary heading valve in accordance with the instant orientation of said fuselage relative to said stationary base, a pneumatically operable member, a pair of pneumatic lines interconnecting said rotary heading valve and said pneumatically operable member, and a connection between said pneumatically operable member and said transmitter, whereby the instant modification of the reading of said instrument is dependent upon the instant positions of said reversible and rotary heading valves.

9. In a grounded aviation trainer of the type including a fuselage rotatably mounted upon a stationary base, rudder pedal means in the fuselage under the control of a student for rotating the fuselage, and an instrument in the fuselage simulating the magnetic compass of a real plane, the combination of means interconnecting the stationary base and said instrument for causing the instrument to register in accordance with the orientation of said fuselage relative to said base, a movable member, means interconnecting said rudder pedal means and said movable member and means interconnecting said stationary base and said movable member for displacing said movable member from its neutral position in a direction dependent upon the combined direction of rotation of said fuselage and instant orientation of said fuselage relative to said stationary base, a connection between said movable member and said instrument for modifying the reading of said instrument in accordance with the position of said movable member, and means for oscillatting the connection between said movable memher and said instrument upon a return of said movable member to its neutral position when said fuselage is oriented relative to said base in certain predetermined positions.

10. In a grounded aviation trainer of the type including a fuselage rotatably mounted upon a stationary base, means in the fuselage under the control of a student for rotating the fuselage, and an instrument in the fuselage simulating the magnetic compass of a real plane, the combination of means interconnecting the stationary base and said instrument for causing the instrument to register in accordance with the orientation of said fuselage relative to said base, a pneumatically operated member, means for displacing said pneumatically operated member from its neutral position in accordance with the instant orientation of said fuselage relative to said stationary base, a first shaft, a universal spring assembly interposed between said shaft and said pneumatically operated member for centering the said member as well as rotating the shaft, a second shaft, a second universal spring assembly interconnecting said two shafts, a connection between said second shaft and said instrument, and means for oscillating said second shaft upon a return of said pneumatically operated member to its neutral position when said fuselage is oriented relative to said base in certain predetermined positions.

KARL A. KAIL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,099,857 Link Nov. 23, 1937 2,164,412 Koster July 4, 1939 2,308,566 Noxon Jan. 19, 1943 2,366,603 Dehmel Jan. 2, 1945 2,443,076 Lowkrantz June 8, 1948 2,460,305 Muller Feb. 1, 1949 FOREIGN PATENTS Number Country Date 396,537 Great Britain 1933 396,538 Great Britain 1933 

